The invention relates to a head operative by conduction response for a meter such as a vacuum gauge, gas thermal-conductivity detector or other such apparatus.
A meter head operative by thermal conduction has a measurement device having thermally-dependent electrical conduction arranged for thermal communication with the material to be metered and electrical conduction in one arm of a bridge circuit, and other electronic components, as appropriate. Two terminals on the meter head are for connecting the meter head to a power supply disposed externally thereof.
The assignee's German patent publication OS No. 31 30 817 and corresponding U.S. Pat. No. 4,492,123 disclose such a thermal-conduction vacuum gauge having a meter head and a separate control unit. The control unit houses a meter and a power supply. The meter head houses a device having thermally-dependent electrical conduction in thermal communication with the vacuum to be gauged and electrically connected into a measuring bridge, as well as other electronic components, including a voltage regulator and an amplifier for processing the bridge-measured values. The meter head and control unit are connected by a two-conductor cable of any desired length. Bothe the power and the measuring current are transmitted through this single cable for improved accuracy.
When plural vacuum gauges of this type are installed in a single plant, however, a disadvantage develops from the common transmission of the measuring current and power supply on the single, two-conductor cable because this requires a separate power supply for each meter head. This is also true of such a vacuum gauge having multiple measurement devices in a single meter head, whether the measurement devices are wire coils with temperature-related resistances, thermocouples, or the like. All-in-all, therefore, the greater the number of vacuum gauges needed in an installation, the greater the cost of the power supplies required.